At the plant, Netanyahu said Iran is a threat to the region and that Tel Aviv could destroy its enemies, based on its nuclear capabilities.

Thursday's letter said Netanyahu's remarks pose "a serious threat to international peace and security," and urged the United Nations to force Israel to comply with international rules.

The letter also demanded the United Nations not only condemn Israel's threat, but also make the country join the Nuclear Non-Proliferation Treaty, and open its nuclear program to International Atomic Energy Agency inspections.

Nasrallah also warned Israel it will get a response it "has never expected" if it wages war with Lebanon, or its ally Iran.

Former Israeli general and National Security Council Chief Yaakov Amidror said he does not expect Iran to leave the 2015 nuclear deal, despite political pressures that followed the United States' departure this year.

"It is the best deal for them," Amidror said. "I would be very surprised if they leave."